Embodiments herein generally relate to electrostatic printing devices and, more particularly, to an electrostatic printing device having multiple steering systems for accurately maintaining lateral alignment of an endless intermediate transfer belt (ITB).
Many multi-color electrostatic printing devices incorporate the use of an endless intermediate transfer belt (ITB). Typically, during an ITB print operation, the ITB passes through multiple different color imaging stations positioned in series along the ITB circumference in order to create a full-color image on the ITB surface. The full-color image is then transferred from the ITB to a print medium (e.g., a sheet of paper) at a belt-to-print medium (BTP) transfer station. Thus, lateral alignment of the ITB is critical to ensure proper image-on-print medium (IOP) registration and proper color-to-color registration. In an attempt to achieve lateral ITB alignment, many printing devices incorporate a belt steering system (also referred to as a belt positioning system, a belt position tracking and correction system, etc.) to reduce deviation of the belt from its desired transport path. Various types of belt steering systems are known in the art. Typically, such belt steering systems use a single steering roller with a tilt mechanism that corrects the lateral position of the ITB, as measured by a belt edge sensor located, for example, adjacent to (i.e., near) the steering roller. Unfortunately, since such belt steering systems make corrections at only one location around the belt circumference, they are not sufficient to maintain the lateral alignment of the ITB as it passes through the multiple imaging stations and through the BTP transfer station. The resulting lateral skew of the ITB, for example, between the steering roller and the BTP transfer station and further between the different imaging stations can result in IOP registration errors and color-to-color registration errors.
In view of the foregoing, disclosed herein are embodiments of an apparatus that uses multiple belt steering systems to control and maintain lateral alignment of an endless belt. For example, the apparatus can comprise a printing apparatus that uses multiple belt steering systems to control and maintain lateral alignment of an endless intermediate transfer belt (ITB). In each of the embodiments, the position of the lateral edge of the belt is measured by multiple belt edge sensors and then corrected by at least two steering rollers connected to corresponding belt steering mechanisms. The belt steering mechanisms tilt the rollers in order to adjust the lateral position of the belt at multiple locations. The steering mechanisms for the rollers can be controlled independently with the tilt of each steering roller being adjusted based solely on information obtain from a corresponding belt edge sensor. Alternatively, the steering mechanisms for the rollers can be controlled dependently with the tilt of each steering roller being adjusted based on information obtain from multiple sensors at multiple locations and further based on the predictable impact of the simultaneous movement of both rollers on belt positioning. In addition, to save space, at least one of the steering rollers can also be configured as a drive roller that causes the belt to travel in a given direction.
More particularly, disclosed herein are embodiments of an apparatus that comprises an endless belt. For example, the apparatus can comprise a printing apparatus (e.g., an electrostatic printer, a xerographic printer, etc.). This printing apparatus can comprise an endless intermediate transfer belt (ITB), a plurality of imaging stations positioned in series adjacent to the outer surface of the ITB and a belt-to-print medium (BTP) transfer station also position adjacent to the outer surface of the ITB. In operation, the ITB can travel in a given direction through the multiple imaging stations in order to create a full-color image on the ITB surface. The full-color image can then be transferred from the ITB to a print medium (e.g., a sheet of paper) at the BTP transfer station.
In order to ensure lateral alignment of the endless belt during operation (e.g., in the case of the printing apparatus described above or in the case of some other apparatus that incorporates the use of an endless belt), the embodiments of the apparatus disclosed herein can comprise multiple steering rollers. Each of these multiple steering rollers can be configured with a discrete corresponding steering mechanism. These steering mechanisms can be controlled, in response to sensor measurements, by either discrete corresponding controllers or a single controller.
Specifically, in the embodiments disclosed herein the endless belt can be supported, at least in part, by multiple steering rollers. That is, the inner surface of the endless belt can contact at least a portion of the outer surface of each steering roller. The multiple steering rollers can comprise at least a first steering roller and a second steering roller that are located at different positions with respect to the belt and that are separated from each other by some predetermined distance. The first steering roller can have a first outer surface in contact with the inner belt surface. The first steering roller can further have a first axle with a first fixed end and a first movable end. The first moveable end can be operatively connected to a first actuator (e.g., a first cam-follower system) capable of moving the first movable end in a given actuation direction such that the first axle and, thereby, the first steering roller tilts (i.e., pivots, moves, etc.) with respect to a first pivot point at the first fixed end. By tilting the first steering roller at a specific angle with respect to the first pivot point as the belt travels over the first steering roller, the lateral position of the belt on the first steering roller can be selectively adjusted. Similarly, the second steering roller can have a second outer surface in contact with the inner belt surface. The second steering roller can further have a second axle with a second fixed end and a second movable end. The second moveable end can be operatively connected to a second actuator (e.g., a second cam-follower system) capable of moving the second movable end in a given actuation direction such that the second axle and, thereby the second steering roller tilts (i.e., pivots, moves, etc.) with respect to a second pivot point at the second fixed end. By tilting the second steering roller at a specific angle with respect to the second pivot point as the belt travels over the second steering roller, the lateral position of the belt on the second steering roller can be selectively adjusted. Thus, in order to maintain lateral alignment of the belt as it travels in a given direction over the rollers, one or more controllers are used to control the movement (i.e., the tilting or pivoting) of the first steering roller with respect to the first pivot point as well as to control movement (i.e., the tilting or pivoting) of the second steering roller with respect to the second pivot point. The different apparatus embodiments disclosed herein vary with respect to how movement of the first and second steering rollers about their respective pivot points is controlled: independently or dependently.
In one embodiment, the apparatus can comprise a first sensor and a second sensor. The first sensor can be positioned at a first location adjacent to the first steering roller and the second sensor can be positioned at a second location adjacent to the second steering roller. The first sensor can determine (i.e., sense, measure, etc.) the position of a lateral edge of the belt at the first location (i.e., can determine a first lateral position of the belt). The first sensor can communicate the first lateral position to a controller. The controller can compare the first lateral position to a desired position for the lateral edge of the belt at that first location. Then, the controller can determine a first pivot angle for moving (i.e., tilting or pivoting) the first steering roller in order to return the belt and, more particularly, to return the lateral edge of the belt at the first location to the desired position. Similarly, a second sensor can determine (i.e., sense, measure, etc.) the position of the same lateral edge of the belt at a second location adjacent to the second steering roller (i.e., can determine a second lateral position of the belt). The second sensor can communicate the second lateral position to a controller. The controller can compare the second lateral position to the desired position for lateral edge of the belt at that second location. Then, the controller can determine a second pivot angle for moving (i.e., tilting or pivoting) the second steering roller in order to return the lateral edge of the belt at the second location to the desired position. In this embodiment, either the same controller or discrete controllers (i.e., a first controller for controlling tilt of the first steering roller and a second controller for controlling tilt of the second steering roller) can be used to compare the measured first and second lateral positions to the desired positions and to determine the required pivot angles. However, such processes are performed independently. That is, the determined pivot angle for the first steering roller is not dependent on the determine pivot angle for the second steering roller or vice versa. Once the controller(s) determine the required pivot angles for the first and second steering rollers, the controller(s) can control the corresponding first and second actuators accordingly in order to move (i.e., tilt, pivot, etc.) the first and second moveable ends to the first and second pivot angles, respectively, and, thereby to adjust belt positioning. Consequently, in this embodiment, the first lateral position of the belt at the first location and the second lateral position of the belt at the second location are independently adjusted.
Alternatively, in another embodiment, a plurality of sensors can determine (i.e., measure, sense, etc.) the positions of the lateral edge of the belt at multiple locations. For example, a first sensor can determine a first lateral position of the edge of the belt at a first location adjacent to the first steering roller, a second sensor can determine a second lateral position of the edge of the belt at a second location adjacent to the second steering roller, and (optionally) additional sensors can determine additional lateral positions of the edge of the belt at additional locations. The sensors can communicate these lateral positions to a single controller. The single controller can compare the positions of the lateral edge of the belt at the multiple locations, as measured, to desired positions for the lateral edge at these multiple locations. Then, in order to return the belt and, more particularly, the lateral edge of the belt at these multiple locations to the desired positions, the controller can determine a first pivot angle for the first steering roller and a second pivot angle for the second steering roller. This determination can be made by the controller based on the predictable impact of movement of both the first steering roller and the second steering roller on belt edge positioning. That is, correcting the position of the belt edge at one location by moving a steering roller may have a predictable impact on the positioning of the belt edge at another location and vice versa. Thus, the best pivot angles for moving the first and second steering rollers in order to achieve the desired lateral belt alignment can be determined based on knowledge of the relationship between the two steering rollers and how their movement in combination will impact belt positioning. Once the controller determines the required pivot angles for the first and second steering rollers, the controller can control the corresponding first and second actuators accordingly in order to move (i.e., tilt, pivot, etc.) the first and second moveable ends to the first and second pivot angles, respectively, and, thereby to adjust belt positioning. Consequently, in this embodiment, the first lateral position of the belt at the first location and the second lateral position of the belt at the second location are dependently adjusted.
In order to optimize space within the printing apparatus embodiments described above, one of the steering rollers (e.g., the first steering roller) can further be configured as a drive roller. Rotation of the drive roller in a given direction (e.g., a counter clockwise direction or, alternatively, a clockwise direction) will cause the belt to travel in that same direction. Movement of the belt in turn can cause the second steering roller to rotate about its axle. In order to configure the first steering roller as a drive roller, a drive motor can be operatively connected to the first axle adjacent to the first fixed end so as to rotate the first steering roller. However, if the first steering roller does function as both a steering roller and a drive roller, the apparatus must further comprise a flexible mount for mounting the drive motor and allowing for movement of the first steering roller with respect to the first pivot point in the presence of the drive motor. This flexible mount, which secures the drive motor within the printing apparatus adjacent to the first steering roller, must be adapted to allow either the entire mount itself or the drive motor within the mount to move (i.e., to be tilted or pivoted) in conjunction with the movement of first steering roller and, more particularly, in conjunction with movement of the first movable end of the first axle of the first steering roller.
These and other features are described in, or are apparent from, the following detailed description.